Scavenging means for internal combustion engines



Aug. 16, 1938. H. ALFARO 2,126,860

SCAVENGING MEANS FOR INTERNAL COMBUSTION ENGINES Filed Oct. 15, 1955 2 Sheets-Sheet 1 III III'I'IIII'IIIIIIIIIIIIA 'Illllllllilltllll'llll INVENTOR Heraclio Alfaro BY M a H. ALFARO Aug. 16, 1938.

SCAVENGING MEANS FOR INTERNAL COMBUSTION ENGINES Filed Oct. 15, 1935 2 Shets-Sheet 2 91/1/1111, \&\

B3--. IIIIIIIIII/fl IIIIIII/III],I/I/I/II/IIIII/III/IIIIIIIIIIII .1. 5.1:.- Ell-i INVENTOR Heraclio Alfaro BY WWM/( C? ATTORNEYS Patented Aug. 16, 1938 UNITED STATES PATENT OFFICE SCAVENGING MEANS FOR INTERNAL COM- BUST'ION ENGINES 12 Claims.

My invention relates to internal combustion engines of the two-stroke cycle type, and more particularly to engines of the type having two opposed pistons per cylinder.

In engines of the type above referred to it is very difficult to effect a complete elimination of the'residual gases during the short interval of time allowed for the exhaust even at comparatively low speeds of operation and the difficulty becomes more pronounced at higher speeds of operation. It is also diflicult to control the scavenging during periods when the engine is idling. Inefiicient scavenging causes dilution of the explosive mixture and results in loss of power.

The present invention has for its object to increase the emciency of the engine by providing means for effecting a uniformly efiective scavenging of the cylinders while the engine is operating at high speed or under heavy load and while the engine is idling.

A further object is to provide means by which efficient scavenging may be obtained with a minimum expenditure of power.

Heretofore, the scavenging action in two-cycle engines has not been very dependable and there has been excessive mixing between the residual gases from the previous working stroke and the air and fuel entering the cylinder. This reduces the power obtainable with a given size cylinder.

Eflicient scavenging becomes more essential in engines where a high output is desired, such as in engines of the air-craft typeincluding engines of the two-stroke cycle type and engines having two pistons per cylinder with uniflow scavenging.

I have found through experiments that by orderly scavenging and charging the cylinder without unduly agitating its contents I can get a more efficient charging using very little if any excess air. I have found also that while a swirl may be desirable from the point of view of smoothness in the explosion of the gases it may not be desirable in some cases from the point of view of scavenging.

Another difficulty in scavenging is due to the resonance or pressurewaves which are created in the pipes leading to and from the cylinders and in its manifolds and surge tanks, if used due to inertia of the gases. Said pressure waves vary in accordance with the natural vibration frequencyof the gases passing through the system, and are. apt to cause great difficulties in connection with the scavenging operation: I have discovered. that this resonance phenomena when properly controlled my be utilized to increase the effectiveness of thev scavenging operation, In

some cases the scavenging action can be improved by the proper control of resonance, to such an extent that effective scavenging may be obtained without the use of any mechanical means for forcing the air into the cylinder.

Another thing I have found through tests is that, when idling, it is desirable to control the scavenging by throttling the exhaust. This might be also desirable for altitude flying in some cases in order to improve supercharging.

With the above and other objects in view, the invention may be said to comprise the device as illustrated in the accompanying drawings, hereinafter described and particularly set forth in the appended claims, together with such variations and. modifications thereof as will be apparent to one skilled in the art to which the invention appertains.

Reference should be had to the accompanying drawings in which:

Figure 1 is a longitudinal section through one cylinder of an engine of the two-stroke cycle type having two piston per cylinder to which the scavenging means of the present invention is applied;

Fig. 2 is a transverse sectional view showing the air inlet ports extending only partially around the cylinder;

Fig. 3 is a section taken on the line indicated at 33 in Fig. 2;

Fig. 4 is a fragmentary sectional view showing the inlet port and vane on an enlarged scale;

Fig. 5 is a top plan view of the port shown in Fig. 4;

Fig. 6 is a section taken on the line indicated at 6-4 in Fig. 2;

Fig. '7 is a sectional view showing exhaust and air intake pipes communicating with the air inlet and exhaust ports which are adjustable to vary theresonating characteristics of thepipes;

'Fig. 8 is a sectional view showing resonator pipes provided with valve controlled openings for varying their resonating characteristics;

Fig. 9 shows a variable volume resonance chamber in one of the pipes;

Fig. 10 showns an exhaust pipe provided with openings so spaced as to eliminate waves of the particular frequencies which interfere with the scavenging operation;

Fig. 11 shows a sound muming sleeve surrounding the perforated exhaust pipe;

Fig. 12 shows concentric perforated pipes for effecting a substantially complete dampening of the pulsations in the exhaust pipe.

Fig. 13 is a sectional view showing a grouping of the cylinders about a. central shaft.

In the accompanying drawings the invention is shown applied to an internal combustion engine of the barrel type in which the cylinders I are in parallel relation and grouped about a central shaft 50 as shown in Fig. 13,-each cylinder having two opposed pistons. The pistons, indicated by reference numerals 2 and 3 are shown at the outer end of their strokes. Each cylinder I may be provided substantially midway between its ends with apertures 4 and 5 in which may be mounted a spark plug and a fuel injection valve.

Adjacent one end thereof each cylinder l is provided with a circumferential row of air inlet ports 6 which are closed by the piston 2' except when the piston. is at or near the end of its stroke and which communicate with an air inlet manifold 7. The row of inlet ports may extend throughout the circumference of the cylinder as shown in Fig. 1 or may extend partially around the cylinder as shown in Fig. 2 where the ports 8a, and 6b are all on the side of the cylinder away from the central engine shaft and communicate with-an inlet manifold M.

Near the opposite end, the cylinder is provided with a circumferential row of exhaust ports 8 which communicate with an exhaust manifold 9. The row of exhaust ports preferably extends only partially around-the cylinder and on the side of the cylinder away from the central engine shaft 50. i

It is desirable that flow of air through the cylinder be so regulated that the initial inrush of air through the inlet ports will substantially clear the cylinder of exhaust gases remaining after an explosion. To this end it is desirable to eliminate insofar as possible, eddy pockets or low pressure spaces which tend to trap the residual gases. Where the air is introduced through radially disposed ports there is" a tendency to create eddy pockets or low pressure spaces adjacent the portion of the cylinder wall to the inner side of the ports and also adjacent the face of the piston.

The extent of the low pressure space adjacent the inner sides of the ports is greatly reduced by providing the ports with faces at the inner sides thereof which are rounded to a streamline form with the radius of curvature gradually increasing toward the interior of the cylinder wall. In order to substantially completely eliminate the eddy pocket or low pressure area along the Wall of the cylinder a vane or airfoil Il may be mounted in some or all of the ports. edge of the airfpil II is blunt and the airfoil tapers toward its inner edge, the side of the airfoil away from the convex face I0 being also convex and the side toward the convex face It] being preferably slightly concave. The airfoil II is spaced from the rounded face It) to provide a slot and the pressure modifying surfaces serve to deflect a substantial portion of the air stream in a substantially axial direction along the inner face of the cylinder wall, the airfoil ll may be 'secured in place by-means of a bracket consisting of a plate I2 secured by screws l3 to the cylinder wall along the inner edges of the opening and a pair of spaced arms l4 integral with the plate l2 and riveted and brazed or welded to the airfoil.

In order to sweep exhaust gases from the space immediately in front of the piston face, at

' least some of the sides of the portslli toward the outer end of the cylinder are preferably straight to permit direct radial flow across the cylinder face. Where the inlet ports are ar'rangedon The outer 2,12c,sao

one side of the cylinder only as shown in Figs. 2 and 3. the ports 6a intermediate the ends of the rows of ports are preferably provided with airfoils ll while the ports 61) at the ends of the row of ports are provided with straight vanes l5 which serve to direct a substantial flow of air radially across the piston face. The outer edges of the ports 6a which are equipped with the airfoils ll may be curved as shown at It in Fig.-3 to direct air obliquely into the cylinder.

An air inlet pipe I I is connected to the air inlet manifold l and an exhaust pipe 18 is connected to the exhaust manifold 9. It has been found that the pipes 11 and I8 provide resonance conduits and that by providing inlet and exhaust pipes of the proper diameter and length resonance characteristics may be obtained such that the scavenging action is greatly aided by the pressure waves set up in the flowing gases. The proper dimensions for the exhaust and inlet pipes for a given engine can readily be determined by experiment. The scavenging efiiciency may, by proper control of the resonance characteristics of the pipes I1 and I 8, be made sufficiently high to enable an engine to be satisfactorily operated without any pump or blower for delivering thecharging air to the engine cylinders. Proper regulation of the resonance in the inlet conduit, in the exhaust conduit, or in both, will enable the inertia of the gases to be utilized in the scavenging operation. a I

It has been found to be advantageous to throttle the intake or the exhaust, or .both the intake and exhaust, when the engine is idling. As shown in Fig. 1, throttling valves l9 and 20 are mounted in. the pipes I1 and I8 close to the cylinder ports and these valves are provided with arms 2| and 22 outside the pipes which are connected by a link 23. One of the valve shafts may be provided with a hand lever 24 by means of which the valves may be simultaneously adjusted. A link 25 connects the arm 22 with the controller 26 of the fuel injection pump 21 which delivers fuel to the injection valves. By adjustment of the lever 24 the fi el output of the pump is reduced and the air inlet and exhaust passages are simultaneously throttled.

Various devices may be employed to facilitate the adjustment of the resonance characteristics of the inlet and exhaust conduits. In Fig. 7 the inlet and exhaust pipes l1 and I8 are shown provided with telescopic sections 28 and 29 which may be adjusted to vary the length of either or both of the pipes until resonance conduits producing the desired pressure wave effects are obtained.

In Fig. 8 of the drawings inlet and exhaust resonance pipes 30 and 3|: are each provided with a series of spaced apertures 32 each adapted to be closed by a valve 33. By opening valves in either of the pipes the resonating characteristics may be changed and by securing certain of the By varying the volume of chamber 36 the resonance characteristics of the conduit .can be adapted to 3 various operating conditions.

In Fig. 10 of the'drawings, there is shown an exhaust pipe42 provided with spaced holes 43.,

By properly spacing the holes 43 waves of the particular frequencies which interfere with scavenging may be eliminated without losing the advantages of the inertia effect in. scavenging.

To dampen the noise of the exhaust pipe 42 one or more concentric pipes 44 of larger diameter provided with holes 45 properly spaced to dampen sound waves may be provided, as shown in Fig. 11.

If desired, the concentric pipes may be enclosed in a casing 46 provided with an outlet 41 as shown in Fig. 12.

It will be apparent that the present invention provides a simple and inexpensive construction by which the engine cylinders are more effectively scavenged, that the displacement of spent exhaust gases with air is facilitated by providing inlet ports designed to eliminate low pressure spaces within the cylinder and that the amount of air required for scaven is greatly reduced by utilizing the pressure wave effect to properly time the pressure impulses and cause themto travel through the cylinder in such a manner as to speed up the scavenging action.

Furthermore, it is to be understood that the particular form of apparatus shown and described, and the particular procedure set forth,- are presented for purposes of explanation and V illustration and that various modifications of said apparatus and procedure can be made without departing from my invention as defined in the appended claims.

What I claim is: 1

1. In an internal combustion engine, a cylinder having axially spaced air inlet and exhaust ports,

- an inlet port having the edge thereof on the side toward the exhaust port formed with a convex face rounded from near the exterior of the port to the inner surface of the cylinder wall, the radius of curvature of said face increasing toward the interior of the cylinder. 7 r

2. In an internal combustion engine, a cylinder having axially spaced air inlet and exhaust ports, an inlet port having the edge thereof on the side toward the exhaust port formed with a convex face rounded from near the exterior of the port to the inner surface of the cylinder wall, and an airfoil mounted in said inlet port and spaced from said rounded face.

3'. In an internal combustion engine, a cylinder having a row of air inlet ports extending partially around the cylinder and an axially spaced exhaust port, certain of said ports having one edge face on the side toward the exhaust port which is convex, and rounded from adjacent the exterior of the port to the interior of the cylinder and provided with an airfoil therein which is spaced from said convex face, other of said ports having flat edge faces and provided with a flat vane therein interposed between and spaced from flat edge faces thereof.

4. In an internal combustion engine, a cylinder having an air inlet port provided with an edge face which is rounded from near the exterior of the port to the inner surface of the cylinder, and an airfoil provided with a convex face on the side thereof away from said rounded face, said airfoil extendingacross the spaced from said rounded'edge.

port and I 5. In an'internal combustion engine of the two- 1 stroke cycle uniflow scavenging type having axially spaced air inlet and exhaust ports, an inlet port having the edge thereof onthe side toward the exhaust port formed with a convex face rounded from near the exterior of the port 'to the inner surface of the cylinder wall, and 'an airfoil in said inlet port spaced from said rounded face and having its convex face on the side thereof away from said rounded face.

6. In an internal combustion engine of the twostroke cycle uniflow scavenging type having a circumferential row of inlet ports and a circumferential row of exhaust ports spaced axially from said inlet ports,,certain of said inlet ports having means for directing currents of air along the cylinder walls toward the exhaust ports and other of said inlet ports being arranged to direct currents of air radially across the cylinder.

'7. In an internal combustion engine of the two-stroke cycle barrel type in which-the cylinders are grouped about a central shaft, each cylinder having two opposed pistons, intake and exhaust ports located adjacent opposite ends of each cylinder, both the intake and exhaust ports of each cylinder being located in that half of the cylinder which is farthest removed from the central shaft.

8. In an internal combustion engine of the two-stroke cycle barrel type in which the cylinders are grouped about a central shaft, each cylinder having two opposed pistons, intake and exhaust portslocated adjacent opposite ends of each cylinder, both the intake and exhaust ports of each cylinder being located in that half of the cylinder which is farthest removed from the central shaft, and flow deflecting vanes in said ine aust ports; ducts for conducting gases to the inlet ports and from the outlet ports, one of said ducts being pierced with spaced holes to-control pulsation of the gases passing through the ducts.

10. In an internalcombustion engine of the two-stroke cycletype, a cylinder having intake and exhaust ports; ducts for conducting gases to the inlet ports and from the outlet ports,- one of said ducts being pierced with spaced holes, and means for closing one or more of the holes.

11. In an internal combustion engine of the two-stroke cycle type, a cylinder having intake and exhaust ports, a'duct having a perforated wall connected to one of said ports and a second duct of larger diameter than the first and surrounding the same, the second duct also having a perforated wall.

12. In an internal combustion two-stroke cycle type, a cylinder having intake and exhaust ports, a duct having a perforated wall connected to one of said ports, a second duct of larger diameter than the-first nd surrounding the same, the second duct also having a perforated wall, and a third duct of larger diameter than thesecond duct and surrounding the same,

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